Uninterruptable Power Supply Systems

Question 1

Many electrical and electronic devices are considered essential to human activities. These devices are called:

Answer 1

Critical Loads

Question 2

Three key components in a basic UPS system:

Answer 2

The rectifier
The battery
The inverter

Question 3

UPS System failures are typically due to what three common causes?

Answer 3

Overloading
High temperature
Faulty Inverter

Question 4

What is often done to accomplish higher reliability in supplying power to critical loads?

Answer 4

Two independent UPS’s are used - a redundant system

Question 5

Static switches, sometimes called solid state switches can operate in Nano seconds. T or F?

Answer 5

False. They can operate in microseconds

Question 6

Each solid state contact of a static switch has what devices?

Answer 6

Two thyristors in anti-parallel (reverse paralell) configuration
Basically two SCR’s

Question 7

What shape waveform does an inverter produce?

Answer 7

Square waveform

Question 8

Name the three common switches associated with a PWM Inverter:
Which is the default?

Answer 8

SCR’s, IGBT’s, BJT’s

Default is IGBT’s

Question 9

A PWM Inverter produces a true sinusodial waveform. T or F?

Answer 9

False. It isn’t a true sinusodial

Question 10

The installation of a UPS system can be divided into what four areas?

Answer 10

Inputs
DC
Outputs
Auxiliaries

Question 11

Batteries of a UPS can be lead acid or nickel cadmium type. T or F?

Answer 11

False. Can only be lead acid, N.C are not used because they require constant charging and discharging to maintain rated capacity.

Question 12

As a good practice, you must ensure that the inverter or UPS system output rating is at least ____ % of the maximum critical load demand.

Answer 12

125%

Question 13

To help prevent short circuits within an Output of an UPS, you should install a high degree of what sort of protection on the critical load wiring?

Answer 13

Mechanical.
Ex: installing cables in conduits

Question 14

The maintenance bypass switch assembly is made up of three circuit breakers labelled what?

Answer 14

MB -Maintenance Bypass
UIP- UPS Input
UOP - UPS Output

Question 15

Cool ambient air enters through the bottom of a UPS. T or F?

Answer 15

False. Its the lower part of the UPS air enters from

Question 16

Why would a UPS have more than one cooling fan installed?

Answer 16

For redundancy, designed for quick replacement without UPS system shutdown.

Question 17

What would an additional UPS display panel be used to indicate?

Answer 17

Alarms such as high temperature and imminent shutdown warning

Question 18

What does a higher ambient temperature do to battery cells? And what does a lower ambient temperature do to battery cells?

Answer 18

Higher - rapid chemical deterioration
Lower - reduces battery output capacity

Question 19

A sealed cell battery has how many years of servicable life?

Answer 19

5 to 10
A vented cell battery has more at 10-15.

Question 20

What guideline should be followed when doing maintenance on an UPS printed circuit board?

Answer 20

Use an anti-static wristband

Question 21

What are the three seperate tests of a load transfer test on a UPS system?

Answer 21

Manual transfer test
Simulate a failure in the inverter test
Overload through a dummy load

Question 22

What sections of a UPS cannot be operated alone for testing purposes?

Answer 22

Inverter
Bypass Switch

Question 23

A static switch has two SCRS connected in anti-parallel. T or F?

Answer 23

True

Question 24

All four solid state switches of an inverter on at the same time would equal:

Answer 24

A short circuit condition.

Question 25

The best method to identify a failed solid state power device is by comparing the dc voltage between the ___________ & ___________ terminals.

Answer 25

Anode & Cathode

Question 26

True or False:
In 3-phase UPS systems, all line and phase voltages are balanced

Answer 26

True

Question 27

What is another name for a static switch?

Answer 27

Solid state switch or By-pass

Question 28

True or False:
There is a noticeable distortion in the waveform during a load transfer of a UPS.

Answer 28

False, though there is a slight distortion at the instant of transfer, it is considered to be negligible.

Question 29

How many solid state switches are in a basic single-phase PWM inverter? And how are the switches connected?

Answer 29

There are 4, and they are connected in two parallel “totem pole” configurations (basically the same configuration as a bridge rectifier)

Question 30

How do you calculate instantaneous voltage of a sine wave?

Answer 30

V ᵢₙₛₜₐₙₜₐₙₑₒᵤₛ = Vₚₑₐₖ x sin θ

Question 31

How do you determine the average voltage of single point of a PWM waveform?

Answer 31

Vavg = Vpeak x (time on/(time on+time off))